Feline Immunodeficiency Virus Is Concentrated in Milk Early in Lactation

We studied mother-to-offspring transmission of feline immunodeficiency virus (FIV), focusing on milk-borne virus transmission in order to assess its similarities to perinatal HIV transmission. We also attempted to evaluate the influence of intragestational treatment with 9-[2-(phosphono-methoxy)-propyl]adenine (PMPA) on virus transmission to offspring. Eleven female cats (queens), chronically infected with FIV-B-2542 and bred to an FIV-negative male, produced a total of 25 viable and 18 nonviable term kittens. Overall, the vertical transmission rate by untreated queens was 22%, similar to that for HIV, which unfortunately precluded adequate assessment of PMPA efficacy. However, at delivery 9 of 10 queens (90%) had higher viral RNA loads in milk (4 × 104 to 4 × 108 viral copies/ml) than in plasma (5 × 103 to 2.5 × 106 viral copies/ml). Conversely, 10 of 11 queens (91%) had lower proviral loads in milk cells (0 to 102 proviral copies/μg DNA) than blood cells (102 to 104 proviral copies/μg DNA). Thus, FIV is...